Due to the increasing water shortages all over the world, an increasing number of the new, large capacity thermal power plants are equipped with air-cooling systems.
There are two main versions of air-cooling systems suitable for power plant cooling, the direct steam condensing in an air cooled condenser, (ACC) and the indirect cooling tower (IDCT) cooling systems. In the direct ACC system the exhaust steam of the steam turbine is introduced into the air cooled steam-air heat exchangers of a mechanical draft cooling tower, whereas the indirect IDCT system uses water cooled condensers (surface or direct contact types), and the warmed cooling water is introduced into the water-air heat exchangers of a mechanical or natural draft cooling tower. The subject of the present invention is related to an advanced spray system of the direct contact (DC) condensers of large capacity indirect IDCT cooling plants
Except the first filling up of the circulating water system, IDCT plants usually don't need any cooling water make up for their operation during the life-time of the power plant they serve. The water to be used for the first filling of the cooling system can be taken from the water treatment plant of the power station, therefore its quality can be the same as that of the feed water of the boiler-turbine circuit. Consequently the cooling water and the steam condensate can be mixed in the condenser, which means that for IDCT plants direct contact, DC condensers can be used.
In DC condensers there are no expensive titanium or stainless steel tubes, the heat from the condensing steam is transferred to the sprayed in cooling water by thin, turbulent water films, produced by the spray system of the condenser. The heat transfer coefficient between the condensing steam and the turbulent water films is extremely high, in the range of 60,000-70,000 W/m2K, whereas that in case of surface condensers is 6000-7000 W/m2K only.
High heat transfer coefficient means small terminal temperature difference (TTD) in the DC condenser. With well-designed spray system 0.5-0.8° C. TTD can be achieved with DC condensers and with surface condensers with economically fair design 3-5° C. can be reached only. A 1° C. decrease in the TTD means 3.3% saving in the investment cost of the whole cooling plant, therefore in case of the above mentioned examples 8.2-13.8 saving in the investment cost is expected by the use of DC condensers instead of surface types.
The cost of the DC condenser itself is about 1/10 that of the surface ones. The above examples well illustrate the importance of a well-designed spray system of the DC condensers.
Accordingly, it is desirable to provide an effective and efficient cooling system.